Mint a terminal identity token

Mints a short-lived identity attestation for DIME Terminal: an ES256 JWT (typ "terminal+JWT", aud "dime-terminal", sub = the account address) signed with a dedicated key published in the JWKS. It proves account identity to the terminal and grants nothing on Paradex itself — no Paradex endpoint accepts it. Requires an interactive session authenticated with the account's own key: readonly/API tokens, RPC tokens and subkey-scoped tokens are rejected. Sub-accounts and vault operators mint attestations for their own address.